oil tank relocation

I seem to remember that the specific gravity of kerosene is 0.7 Kg per litre and assuming that 1/2 a tank is 500 litres then you are talking about 350 Kg or about 1/3 of a metric ton or 4 big men or 7 hundredweight in old measure.

You could add another 30 or 40 Kg for the empty tank and come up at 400 Kg.

As mentioned above this weight has to be evenly distributed on a flat surface usually prestressed concrete lintels laid over a pair of solid concrete block walls about 1.5 to 2 meters apart.

If the tank bursts and the fuel enters a watercourse or drain the EPA will be out for blood........

Wait until tank is empty or, if you can afford the space, put the new empty tank on a new site adjacent to existing tank, divert the fuel line from the old tank to the new tank. The quarter turn valve at the tank outlet should be turned at right angles to the supply pipe to turn off the oil supply while this plumbing is carried out. All plumbing should be carried out with fuel line tape on the joints, ask the supplier for diesel tape. Ordinary water ptfe tape will not do as fuel attacks the plastic in the tape. Do not overtighten joints at first installation, much better to place cans on strings near joints to collect any drips an tighten slowly over a few weeks until any dripping or sweating stops. Brass threads can be very easily broken or stressed by over tightening

The supply can be verified as off by disconnecting the flexible supply line at the burner with a suitable container underneath to catch any spills. This is very tricky work indoors with indoor boilers because of the risk of spillages and smells but not so bad in a shed, garage or outhouse boiler.

Oil tank suppliers usually can provide a truck tank as temporary storage for any fuel when swapping out old tanks for new.